Fuse integrity indicator



March 13, 1934.

F. c. LA MAR 1,951,310

FUSE INTEGRITY INDICATOR Filed Jan. 17, 1933 1 75 29 mimg w I flza ATTORNE Patented Mar'. 13, 1934 UNITED STATES PATENT OFFICE 3 Claims.

This invention relates to electrical devices, particularly to thermal fuses for use in connection with electrical circuits, and more especially to what is known as a plug fuse, combined with 6 means for indicating the integrity of the fusible element.

It is quite universally known that it is necessary to protect electrical circuits by means of devices, such as thermal fuses, which melt or become disintegrated or destroyed when an excessive fiow of current passes through the circuit of which the fuse forms a part. An especially well known form of thermal fuse is that known as a plug fuse. Ordinary plug fuses consist, gen- 10 erally, of an insulating body having two terminals on the outside thereof, so constructed and arranged as to be readily brought in contact with the terminals of an electrical circuit, by way of what is known usually as a fuse block. These 80 fuses are universally used; are made by many different manufacturers; and must all be usable in practically any of the well known forms of fuse blocks; so that they have become, in truth, standard, and may well be referred to as, standard fuse plugs. At any rate they are substantially standard as regards their general external dimensions.

Various forms of plug fuses have been made, especially for the purpose of enabling one to rapidly discern whether or not the fusible or thermal element is intact. It is quite the universal impression that success has not been fully attained in regard to the feature of indicating the integrity of the fusible element.

A principal object of applicants invention is to provide a device, which may well be called a combined fuse and fuse integrity indicating device. In providing such a device, applicant has had in mind that it preferably should be in external dimensions substantially the size of the standard plug fuse, so that it may be used with a facility equal to that of a standard plug fuse in those situations where a standard plug fuse is now used.

A further object which applicant has in mind in producing his combined fuse and fuse integrity indicator is that the cost must be reduced to a point where, if possible, it approximates the present cost of ordinary plug, fuses. To this end, applicant has, as a further object of his invention, the production of a device in two parts, separable one from the other, one part supporting and protecting the thermal element, which part is removable, and the other part performing the indicating functions desired by applicant,

trate the invention, reference will be had to the accompanying drawing and the several views thereon, in which like characters of reference designate like parts throughout the several views, and in which:

Figure 1 is a front elevational view of my combined fuse plug and fuse integrity indicator, with the thermal element receiving portion shown separated from the indicating portion; Fig. 2 is a top plan view of the indicating portion of the device as shown by Fig. 1; Fig. 3 is a top plan view of the thermal element carrying device as shown by Fig. 1; Fig. 4 is a cross-sectional view on the plane indicated by the line IV-IV of Fig. 2 viewed in the direction of the arrows at the ends of the line; Fig. 5 is a top plan view of the indicating portion of applicants combined fuse plug and fuse integrity indicator as shown in Fig. 1, but with a protector for the indicating lamp removed; Fig. 6 is a cross-sectional view on the plane indicated by the line VIVI of Fig. 2 viewed in the direction of the arrows at the ends of the line; Fig. '7 is an exploded view of the parts as shown by Fig. 1; Fig. 8 is an enlarged detail view illustrating the construction of a spring contact used in the device of Fig. 1; Fig. 9 is a part side elevational and part cross-sectional view corresponding to Fig. 4 but showing a modified form of construction.

Applicants device includes, generally, a thermal element supporting portion T and a ther- 1 formed of insulating material; a threaded shell I 2; a lamp 3; and a metal finger 4.

7 disc 1.

The disc-like member 1 has a depression 10 in one face thereof and projections 11 and 12 on the other face thereof. The depression or cavity 10 serves to receive and retain the metallic shell 2. The projections 1.1 and 12 serve to hold the lamp protector 13 in place.

The metal shell 2 is substantially a hollow cylinder the walls of which for a greater part of the distance have been rolled into the form of a screw thread 14. One end of the hollow metallic shell 2 has a portion bent over to form the annular flange 15 bearing against the bottom of the cavity 10 and serving to make contact with the top of the sleeve cap 8.

The metallic finger 4 is secured in any appropriate or suitable way to the disc 1 as by having it pass therethrough, as shown in Fig. 6, and then expanded.

Within the lamp cover 13 is positioned a lamp 3 and a resistance 1'7. The lamp 3 is preferably of the discharge type and preferably filled with neon so that it emits a distinctive reddish colored light when operated. The resistance 1'? is preferably of the well known grid leak type and serves to prevent such a flow of current through the lamp 3 as to cause it normally to light when the thermal element 9 is intact and also prevents at any time more than a very small quantity of current from flowing.

In order to protect the lamp 3 and the resistance 17 applicant has provided the lamp protector 13 which is formed preferably of insulating material hollow and with a lamp viewing slit at 16. On the inner portion of one side wall is a projection 18 positioned to cooperate with a corresponding projection 19 on the portion 11 of the disc 1. On the other side wall is a pro jection 20 positioned to cooperate with a corresponding projection 21 on the member 12 of the The side walls of the body 13 are made so as to be springy or resilient so that after the lamp 3 and the resistance 17 are in place, the protector 13 may be placed thereover and snapped down into place with its projections under the projections of the members 11 and 12 so that it is securely held in place.

The cylindrical hollow body 5 having an end wall 22 is formed with an opening 23 through the end wall. In the opening is placed the hollow rivet 24, formed preferably of a metal such as brass. After the hollow rivet 24 is put in place the upper end of the wall thereof is bent over so as to form an annular flange 25 which secures the hollow rivet.

The hollow guiding column '7 has a small portion of metallic tube 26 inserted in the end thereof, and in this hollow tube is placed the helical spring 6. The helical spring 6 is attached to the tube 26 at its lower end and the tube 26 is conductively attached to hollow rivet 24 by filling in the space 27 with solder.

In order to hold the hollow guiding column 7, at the top, central of the hollow body 5, applicant provides an enlargement or disc shaped member 28 at the upper end of the member '7. This disc 28 just fits nicely within the metallic sleeve 8 so that when the metallic sleeve 8 is in place the disc is central of the hollow body 5 and so is the hollow guiding column 7.

The metallic sleeve 8 which caps the hollow body 5 makes a fit on the outside of the hollow body 5 tight enough to be thereby retained in place. The sleeve 8 is provided with struck-up portions 29 which make more certain good metallic contact between the flange 15 of shell 2 and the cap 8.

The thermal element 9 is of the ordinary type of fusible element and is soldered at one end at the point 30 to the hollow rivet 24, the tube 26, and the spring 6 and at its other end is soldered at the point 31 to the lower edge of the metallic sleeve cap 8.

The upper edge of the hollow body 5, as best shown in Fig. '7, is formed with openings or slots, as 32. These slots serve as a means by which gases generated by the fusing and volatilization of thermal element 9 may escape along the space between the metal cap 8 and the outer s niece of the member 5.

If desired, a small disc 33 may be positioned between the disc like portion 28 and the cap 8 upon which any desired indicia may be placed, such as the rating of the fusible element 9.

The hollow body 5 is formed on its outer surface with the screw thread 34 of the same pitch and size as the screw thread 14 of the member 2. When the thermal element carrying portion T is assembled, as shown in Fig. 1, it may then be combined with the indicating portion I of Fig. 1 by screwing the portion T therein so that the parts come into the position as shown in Fig. 4.

When the parts are in the position, as shown in Fig. 4, one side of the circuit is the hollow rivet v 24, the other, the metallic shell 2. These are connected directly by the fusible element 9.

The lamp 3 has one terminal connected by the wire 35 to the grid resistance 1'7. The other terminal of the lamp is connected by conductor 36 to the metallic finger 4. The other side of the grid resistance 1'7 is connected by the conductor 37 to the shell 2 at the point 38 by means of a drop of solder. The lamp, as described, is connected in parallel or in shunt to the thermal ele ment 9. When the thermal element is intact, the lamp is not lighted. When the thermal element is disrupted, the current then flows through the lamp and causes it to become illuminated.

If the thermal element 9 is disrupted, applicant contemplates that the entire member T will be removed, discarded, and a new member T screwed into place into the shell 2, that is, into the thermal element integrity indicator carrying portion I.

In Fig. 9, a construction somewhat modified is shown. In this construction a different form of sleeve corresponding to the sleeve 8 is used. The different form of sleeve 39 is made of such length that a thread 40 may be formed therein to cooperate with a thread 41 on the body 42. The member T of Fig. 9 is put into place cooperating with the member I by screwing the sleeve 39 into the shell 2, but the cooperating parts are the sleeve 39 through its thread 40 thereon and the threads of the shell 2. This form of construction gives a better electrical contact between the sleeve 39 and the shell 2.

Although I have particularly described one particular physical embodiment of my invention and explained the operation, construction, and principle thereof, nevertheless, I desire to have it understood that the form selected is merely illustraive but does not exhaust the possible physical embodiments of the idea of means underlying my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. As in indicating portion of a combined thermal fuse and fuse integrity indicator; an insulating body approximately a disc and formed with a cavity in one face for the reception of one end of a metallic shell and on the other face with shouldered projections for securing a lamp protector; a metallic shell corrugated to form a helix having one end flanged and positioned in the cavity in one face of the body bearing against the side walls thereof whereby the shell is held securely in place; a metallic finger positioned centrally of the shell, supported by the hollow body, and adapted for contact with a terminal of a thermal element supporting body; a lamp positioned between the shouldered projections on the other face of the insulating body and having terminals, one connected to the metallic shell and the other to the metallic finger; and a lamp protector formed as a hollow body with an observation slit therethrough and with shoulders cooperating with the shoulders on the projections of the insulating body whereby the lamp protector may be held in place.

2. As the thermal element supporting body oi a separable combined thermal fuse and fuse integrity indicator; a substantially cylindrical hollow body of insulating material formed on its curved surface with a helical projection forming a screw thread; a metallic sleeve formed with a helix corresponding with the helical projection of the insulating body and screwed in place thereon and at one end formed with an annular flange extending over the edge of the hollow body, said metallic shell adapted to cooperate and make contact with a metallic shell of a fuse integrity indicator; a metallic terminal positioned at one end of the hollow body adapted to make contact with one side of an electric circuit to be protected; a metallic tube containing a spring attached to the said metallic terminal, said metallic spring adapted for contact with a contact finger of a fuse integrity indicator; a hollow guiding column supporting one end of the metallic tube and formed on the other end into the form of a centering disc cooperating with the metallic sleeve; a thermal element connecting the terminal and the metallic sleeve.

3. In a combined thermal fuse and fuse integrity indicator, as a contacting means between the thermal element supporting portion and the indicator supporting portion, the combination: of a hollow metallic rivet adapted to receive molten solder; a metallic tube containing within its bore a helical metallic spring, a short portion of the tube and spring being positioned within the hollow of the hollow rivet; a hollow guiding column receiving the other end of the tube and supporting and guiding the same; means for pcsitioning and holding the hollow guiding column relatively to the hollow rivet; a thermal element, one end of which is positioned in the hollow of the hollow rivet; and means for connecting the other end of the thermal element to one side of a circuit to be protected.

FRANK C. LA MAR. 

